1. Field of the Invention
This invention relates to improvements in a catalytic converter including a ceramic catalyst carrier to be used to purify exhaust gas from an internal combustion engine and in a method of producing the catalytic converter. More particularly, the invention relates to the improvements by which the ceramic catalyst carrier is axially supported at a predetermined or constant pressure within a metal container.
2. Description of the Prior Art
A variety of catalytic converters have been proposed and put into practical use for internal combustion engines. At typical one of them is disclosed in Japanese Utility Model Provisional Publication No. 57-191818 and schematically shown in FIG. 10. This catalytic converter includes a generally cylindrical ceramic carrier 123 which is made of a ceramic and carries a catalytic material. The ceramic carrier 123 is encased in a container 120 made of a metal. The container 120 is formed with converged section 121, 121 to support thereinside the ceramic carrier 123 through cushioning materials 122, 122 which are formed of metal wire mesh. Additionally, a supporting material 124 formed of metal wire mesh and a thermally expandable sealing material 125 are wound on the ceramic carrier 123 at the outer peripheral surface. The supporting material 124 is fitted inside the container 120.
The catalytic converter of this type has the following defects: The converged sections 121, 121 of the container 120 are formed by pressing, and therefore a distance or axial dimension between the converged sections 121, 121 are not uniform throughout products (catalytic converters). Accordingly, a supporting force for the ceramic carrier 123 cannot be maintained constant throughout the products. Additionally, the axial dimension of the ceramic carrier 123 is not uniform throughout the products. As a result, it is very difficult to encase the ceramic carrier 123 within the container 120 and maintain a constant supporting force.
In order to solve the above problem, it has been proposed to omit the converged sections 121, 121 as disclosed in Japanese Utility Model Provisional Publication No. 58-37916 and Japanese Patent Provisional Publication No. 55-64111.
A catalytic converter as disclosed in Japanese Utility Model Provisional Publication No. 58-37916 is arranged as follows: Annular metal caps are fixedly attached to the inner surface of a container made of a metal, in place of the converged section omitted, thereby determining the position of a ceramic catalytic carrier within the container. The ceramic carrier is kept or supported within the container through a foamed cushioning material formed from inorganic material, disposed between the container and the ceramic carrier.
With the catalytic converter of this type, the supporting force for the catalytic element can be prevented from being not uniform. However, even this catalytic converter has not yet solved the problem that the supporting force for the catalytic element becomes non-uniform throughout the products (catalytic converters) thereby lowering the supporting force. Furthermore, the foamed cushioning material formed from the inorganic material tends to be scattered in ambient air under flowing of gas through the catalytic converter, which is a defect of this catalytic converter. In view of the above fact, this catalytic converter requires a shield member for sealing the cushioning material from a gas flowing passage in the catalytic converter thereby preventing the cushioning material from being scattered. This unavoidably increases the number of constituting parts and steps of a production process of the catalytic converter. In addition the catalytic converter cannot prevent the cushioning material from being scattered, thus resulting in a shorter life span for the converter
The catalytic converter disclosed in Japanese Patent Provisional Publication No. 55-64111 is shown in FIGS. 11 and 12 and is provided with annular metal caps 130, 130 which are fixedly attached to the inner surface of a container 134 similar to that disclosed in Japanese Utility Model Publication No. 58-37916, in order to determine the position of a ceramic catalyst carrier 131. The ceramic carrier 131 is axially securely supported by the annular metal caps 130, 130 through cushioning materials 132, 132 which are produced by an annular metal wire mesh, each interposed between each annular cap 130 and the catalyst carrier 131.
In this catalytic converter, a cylindrical cushioning material 133 is disposed between the outer peripheral surface of the ceramic carrier 131 and the inner peripheral surface of the container 134. Annular cushioning materials 132, 132 are disposed at outer peripheral portions of the opposite ends of the ceramic carrier 131. Pressing members 135 are disposed to press and connect the cylindrical cushioning material 133 and the annular cushioning material 132, 132 under incorporation of the metal caps 130, 130. When the cylindrical cushioning material 133 is located at a suitable position, the pressing member 135 and the metal cap 130 are welded to the metal container 134, thus securely encasing the ceramic carrier 131 within the metal container 133.
However, even the production of the catalytic converter in Japanese Patent Provisional Publication No. 55-64111 does not take into account the fact that the dimension of the axial length of the ceramic carrier 131 is not uniform throughout products (ceramic carriers). Accordingly, when the cylindrical cushioning material 133 is located at the suitable position, the connected pressing member and metal cap 135, 130 are welded to the metal container 134, even if any pressure is applied from the annular cushioning material 132 to the ceramic carrier 131. Consequently, a supporting force for the ceramic carrier 131 is not always constant or uniform throught the products.